Currently, if you go to the XBOX.com site there is an option in "MY XBOX" to give you some FRAME code to add your Gamer card to web sites. That works fine on your website, as you can see I added it to mine at HSDEMONZ.com

However, if you want to add it to your signature here on XS you'll have a slight problem. We won't/don't support that code that handles that in the signature. However, there are a number of currently free services, that are providing a JPG version of your card that can be easily displayed in your signature, and the JPG updates frequently.

In the examples that follow replace HSDEMONZ with your name. If you have a space in your Gamer tag at %20 to represent the space.